Is it possible to automatically display all profiles in a gallery?
Using Jamroom
Yes, sent me up a bag.

Not much space to garden up here.
1.) you can add any additional search fields you would also like covered in the search by adding them to:
ACP -> LISTING -> SEARCH -> GLOBAL CONFIG -> additional Search Fields
Quote: If you would like to have additional DataStore fields available for search, enter the DataStore field name, one per line.
Example:
If you have created a custom User Profiles field via the Form Designer called "profile_location" you would enter profile_location on a line by itself to enable that field to be searched.
2.) sounds like a job for the Quota system, but the use case description makes it hard to give exact instruction. The steps to take to setup a new quota are to first decide which modules will be active on profiles in each quota. Feels like what your after is a bunch of profiles that the admin has created in one quota, then user signups to a second quota. The admin then assigns users to be able to access the first quotas profiles on an individual case. Might need a custom module if you want them to grant themselves access.
3.) You can specify the quota ID as one of the search fields when using the {jrSearch_module_form} function. eg:
{jrSearch_module_form fields="audio_title,audio_album,audio_genre" search1="profile_quota_id = 1"}
That would only search the audio_title,audio_album,audio_genre fields created by users in the quota id '1'
You could put that in any template where you wanted to see the search form.
The thing with Jamroom is that one of the premises its built on is: Keep the core features to a minimum and let the user expand it because its easier to add features than it is to take un-wanted features away.
So unless its going to be wanted in every case, its probably not going to become a core feature.
But thats ok because skin designers are not limited by that premise and they can build custom skins that override/extend core functionality. So while it may not become a core feature, there might be a skin designed containing that feature.